1. Field of the Invention
The present disclosure relates to a drive transmission device, a fixing device, and an image forming apparatus including a one way clutch mechanism that transmits or cuts off a driving force, input from a drive source, to a driven member, in accordance with a rotation direction.
2. Description of the Related Art
Some drive transmission devices, for a fixing device of an image forming apparatus, include a one way clutch mechanism. The one way clutch mechanism uses a drive source (motor), rotatable in normal and reverse directions, to transmit the driving force to a driven member when the motor is rotating in only one of the normal or reverse direction. One such one way clutch mechanism includes a transmission member (ratchet) that is disposed between coaxially rotatable input and output members. The transmission member can rotate together with the input member, and move in a rotational axis direction. In the mechanism, engaged and disengaged states of the transmission member and the output member are switched in accordance with the normal/reverse rotation of the input member.
A configuration for reducing the noise during a state where the transmission member is not engaged with the output member (when the transmission member is idling) is discussed in Japanese Patent Application Laid-Open No. 7-61619. Specifically, a cam surface is provided at a position of contact between the input member and the transmission member. Thus, when the input member rotates, the transmission member is moved toward the output member in a rotational shaft direction by the effect of the cam surface. Thus, the transmission member engages with the output member, whereby the driving force is transmitted from the input member to the output member through the transmission member.
In the configuration discussed in Japanese Patent Application Laid-Open No. 7-61619, a rotational load needs to be applied to the transmission member to make the transmission member move in the rotational axis direction by the effect of the cam surface. This is because the transmission member is forcibly rotated upon receiving force from the input member through the cam surface.
As one possible method of applying the rotational load, a gap between the output member and the transmission member is filled with a viscous material having a viscous force. With this method, a force for holding the transmission member in the rotation direction (force for preventing the rotation of the transmission member) can be produced between the output member and the transmission member. Thus, the transmission member can be moved in the rotational axis direction by the effect of the cam surface to engage with the output member.
However, when the gap between the output member and the transmission member is simply filled with the viscous material, the viscous material has no place to go when the output member comes into contact with the transmission member, and thus might flow into a gap between the input member and the transmission member. When this happens, the input member attaches to the transmission member by the viscous force of the viscous material. Thus, the transmission member integrally rotates with the input member, before being moved in the rotational axis direction by the effect of the cam surface. Thus, the transmission member cannot be moved in the rotational axis direction by the effect of the cam surface, and thus the driving force might fail to be transmitted to the output member.